Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
  • F02D—CONTROLLING COMBUSTION ENGINES
  • F02D19/00—Controlling engines characterised by their use of non-liquid fuels, pluralities of fuels, or non-fuel substances added to the combustible mixtures
  • F02D19/02—Controlling engines characterised by their use of non-liquid fuels, pluralities of fuels, or non-fuel substances added to the combustible mixtures peculiar to engines working with gaseous fuels
  • F02D19/021—Control of components of the fuel supply system
  • F02D19/022—Control of components of the fuel supply system to adjust the fuel pressure, temperature or composition
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
  • F02D—CONTROLLING COMBUSTION ENGINES
  • F02D19/00—Controlling engines characterised by their use of non-liquid fuels, pluralities of fuels, or non-fuel substances added to the combustible mixtures
  • F02D19/02—Controlling engines characterised by their use of non-liquid fuels, pluralities of fuels, or non-fuel substances added to the combustible mixtures peculiar to engines working with gaseous fuels
  • F02D19/021—Control of components of the fuel supply system
  • F02D19/023—Control of components of the fuel supply system to adjust the fuel mass or volume flow
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
  • F02D—CONTROLLING COMBUSTION ENGINES
  • F02D19/00—Controlling engines characterised by their use of non-liquid fuels, pluralities of fuels, or non-fuel substances added to the combustible mixtures
  • F02D19/02—Controlling engines characterised by their use of non-liquid fuels, pluralities of fuels, or non-fuel substances added to the combustible mixtures peculiar to engines working with gaseous fuels
  • F02D19/026—Measuring or estimating parameters related to the fuel supply system
  • F02D19/027—Determining the fuel pressure, temperature or volume flow, the fuel tank fill level or a valve position
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
  • F02D—CONTROLLING COMBUSTION ENGINES
  • F02D19/00—Controlling engines characterised by their use of non-liquid fuels, pluralities of fuels, or non-fuel substances added to the combustible mixtures
  • F02D19/06—Controlling engines characterised by their use of non-liquid fuels, pluralities of fuels, or non-fuel substances added to the combustible mixtures peculiar to engines working with pluralities of fuels, e.g. alternatively with light and heavy fuel oil, other than engines indifferent to the fuel consumed
  • F02D19/0602—Control of components of the fuel supply system
  • F02D19/0605—Control of components of the fuel supply system to adjust the fuel pressure or temperature
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
  • F02D—CONTROLLING COMBUSTION ENGINES
  • F02D41/00—Electrical control of supply of combustible mixture or its constituents
  • F02D41/0025—Controlling engines characterised by use of non-liquid fuels, pluralities of fuels, or non-fuel substances added to the combustible mixtures
  • F02D41/0027—Controlling engines characterised by use of non-liquid fuels, pluralities of fuels, or non-fuel substances added to the combustible mixtures the fuel being gaseous
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
  • F02D—CONTROLLING COMBUSTION ENGINES
  • F02D41/00—Electrical control of supply of combustible mixture or its constituents
  • F02D41/30—Controlling fuel injection
  • F02D41/38—Controlling fuel injection of the high pressure type
  • F02D41/3809—Common rail control systems
  • F02D41/3836—Controlling the fuel pressure
  • F02D41/3845—Controlling the fuel pressure by controlling the flow into the common rail, e.g. the amount of fuel pumped
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
  • F02D—CONTROLLING COMBUSTION ENGINES
  • F02D41/00—Electrical control of supply of combustible mixture or its constituents
  • F02D41/30—Controlling fuel injection
  • F02D41/38—Controlling fuel injection of the high pressure type
  • F02D41/3809—Common rail control systems
  • F02D41/3836—Controlling the fuel pressure
  • F02D41/3845—Controlling the fuel pressure by controlling the flow into the common rail, e.g. the amount of fuel pumped
  • F02D41/3854—Controlling the fuel pressure by controlling the flow into the common rail, e.g. the amount of fuel pumped with elements in the low pressure part, e.g. low pressure pump
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
  • F02D—CONTROLLING COMBUSTION ENGINES
  • F02D41/00—Electrical control of supply of combustible mixture or its constituents
  • F02D41/30—Controlling fuel injection
  • F02D41/38—Controlling fuel injection of the high pressure type
  • F02D41/40—Controlling fuel injection of the high pressure type with means for controlling injection timing or duration
  • F02D41/402—Multiple injections
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
  • F02M—SUPPLYING COMBUSTION ENGINES IN GENERAL WITH COMBUSTIBLE MIXTURES OR CONSTITUENTS THEREOF
  • F02M21/00—Apparatus for supplying engines with non-liquid fuels, e.g. gaseous fuels stored in liquid form
  • F02M21/02—Apparatus for supplying engines with non-liquid fuels, e.g. gaseous fuels stored in liquid form for gaseous fuels
  • F02M21/0218—Details on the gaseous fuel supply system, e.g. tanks, valves, pipes, pumps, rails, injectors or mixers
  • F02M21/023—Valves; Pressure or flow regulators in the fuel supply or return system
  • F02M21/0239—Pressure or flow regulators therefor
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
  • F02M—SUPPLYING COMBUSTION ENGINES IN GENERAL WITH COMBUSTIBLE MIXTURES OR CONSTITUENTS THEREOF
  • F02M21/00—Apparatus for supplying engines with non-liquid fuels, e.g. gaseous fuels stored in liquid form
  • F02M21/02—Apparatus for supplying engines with non-liquid fuels, e.g. gaseous fuels stored in liquid form for gaseous fuels
  • F02M21/0218—Details on the gaseous fuel supply system, e.g. tanks, valves, pipes, pumps, rails, injectors or mixers
  • F02M21/0245—High pressure fuel supply systems; Rails; Pumps; Arrangement of valves
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
  • F02D—CONTROLLING COMBUSTION ENGINES
  • F02D2200/00—Input parameters for engine control
  • F02D2200/02—Input parameters for engine control the parameters being related to the engine
  • F02D2200/06—Fuel or fuel supply system parameters
  • F02D2200/0602—Fuel pressure
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
  • Y02T10/00—Road transport of goods or passengers
  • Y02T10/10—Internal combustion engine [ICE] based vehicles
  • Y02T10/30—Use of alternative fuels, e.g. biofuels

Definitions

• This invention generally relates to fuel systems and control systems for fuel systems. More particularly, this invention relates to fuel systems and method involving gaseous fuel.
• the gaseous fuel system 100 includes a mechanical pressure regulator 110 that controls the flow of a gaseous fuel into a fuel rail 120.
• the fuel rail 120 distributes the gaseous fuel to a plurality of gas admission valves 130.
• the gas admission valves 130 are controlled by a controller 140 that receives a mass flow demand and sets the duration of the opening and closing of the gas admission valves 130 to correspond to the mass flow demand.
• the mechanical pressure regulator 110 is set at a desired fuel pressure for pressurizing the fuel rail 120.
• the gaseous fuel takes time to fill the fuel rail 120, and because the controller 140 does not know the pressurization status of the fuel rail 120, the system 100 can become overpressurized or underpressurized. That is, when the controller 140 opens and closes the gas admission valves 130, a greater or lesser quantity of gaseous fuel than desired may be delivered to the downstream fuel manifold (not shown) or engine cylinder (not shown).
• gaseous fuel systems 100 can, under certain circumstances, experience pressure droop from the mechanical pressure regulator 110, including even mechanical pressure regulators 110 configured to correct using electronic I/P adjustment mechanisms.
• This pressure droop can limit the applicable operational range of the gas admission valves 130.
• the fixed pressure setting from the mechanical pressure regulator 110 can cause low opening durations for the gas admission valves 130 at low engine loads, which causes fuel flow inaccuracy.
• this system configuration makes adequate protection of the gas admission valves 130 (and the entire system downstream of pressure regulator) from over pressurization difficult during the initial pressurization of the gaseous fuel system 100.
• Yet another potential disadvantage of this system configuration relates to the difficulty of determining the gas substitution percentage in dual fuel engines as a result of the gas admission valve 130 inaccuracy mentioned above.
• Embodiments of the presently disclosed system and method address the difficulties of determining the pressurization of a gaseous fuel system so as to protect components of the system and to provide accurate fueling.
• embodiments of the presently disclosed invention provide a gaseous fuel system and method having coordinated control between an engine controller, an electronic pressure regulator, and the gas admission valves.
• the controller is provided with certain physical parameters of the gaseous fuel system including system volume, gas admission valve duration, and engine fuel demand.
• system volume system volume
• gas admission valve duration gas admission valve duration
• engine fuel demand engine fuel demand.
• both pressure and mass flow are able to be controlled independently through an electronic pressure regulation system.
• mechanical regulator pressure droop is eliminated by controlling pressure to the gas admission valves in a range that is optimized for their performance at a given fuel flow.
• the fuel system experiences an improvement in turn down, potentially reducing the number of gas admission valve sizes required in the system.
• the system is able to operate at a minimum optimum pressurization so as to maximize the duration of the gas admission valves regardless of the load point. In this way, the accuracy and the repeatability of the system performance is enhanced.
• a further advantage of the disclosed system and method relates to prevention of over-pressurization and under-pressurization of the fuel system downstream of the electronic pressure regulator through flow and pressure control.
• pressurization conditions are created when a large differential pressure is created in the system, such as, for example, during the system’s initial start-up filling transient, when a breaker trips causing the engine to go from full load to no load, or when the system is shut down and the shutoff valve is located far upstream of the fuel rail.
• Such events can create a pressure differential over the operational limit of the gas admission valves.
• the presently disclosed system and method avoid such pressurization events by using the electronic pressure regulator to provide a faster response to rail pressure during such events. Additionally, the electronic pressure regulator does not have to start in a normally open condition, which minimizes the likelihood of overpressurization.
• embodiments of the invention provide a method of regulating flow of a gaseous fuel in a multipoint fuel injection system.
• a fuel rail provides the gaseous fuel to a plurality of gas admission valves.
• a first mass flow of the gaseous fuel is estimated entering the fuel rail using an electronic pressure regulator.
• a second mass flow of the gaseous fuel is determined exiting the fuel rail.
• a rate of pressure change in the fuel rail is calculated as a function of a difference between the second mass flow and the first mass flow.
• at least one of a first effective area of an electronic pressure regulator or a pulse duration of the plurality of gas admission valves is adjusted in response to the calculated rate of pressure change.
• a gaseous fuel regulation system includes a fuel rail, an electronic pressure regulator (EPR), a plurality of gas admission valves, and an engine control unit (ECU).
• the EPR is upstream of and in fluid communication with the fuel rail, and the EPR is configured to meter a first mass flow of a gaseous fuel flowing through the EPR.
• Each gas admission valve is downstream of and in fluid communication with the fuel rail.
• the ECU is configured to receive a mass flow delivery command and to set a first effective area of the EPR and a second effective area of the plurality of gas admission valves based at least in part on the mass flow delivery command and on the first mass flow.
• inventions of a dual fuel system include a first fuel rail carrying a liquid fuel, a second fuel rail carrying a gaseous fuel, and a plurality of engine cylinders.
• the liquid fuel and the gaseous fuel are combusted in the plurality of engine cylinders, and the flow of the gaseous fuel to the plurality of engine cylinders is controlled by the gaseous fuel regulation system as described above and in greater detail below.
• FIG. 1 is a schematic depiction of an electronic pressure regulator system, according to an exemplary embodiment
• FIG. 2 is a simplified depiction of the electronic pressure regulator, fuel rail, and gas admission valves, according to an exemplary embodiment
• FIG. 3 is a schematic depiction of the control configuration of the electronic pressure regulation system, according to an exemplary embodiment
• FIG. 4 is a schematic depiction of a first order filter for determining the rate of fuel rail pressure change, according to an exemplary embodiment
• FIG. 5 is a graphical representation of the responses of the gas admission valves and electronic pressure regulator to a change in mass flow demand, according to an exemplary embodiment
• FIG. 6 is a graphical representation of the response of the actual rail pressure to a change in a reference pressure resulting from the change in mass flow from FIG. 5, according to an exemplary embodiment
• FIG. 7 is a graphical representation of change in effective area for the gas admission valves and the electronic pressure regulator resulting from the change in mass flow from FIG. 5, according to an exemplary embodiment
• FIG. 8 is a prior art depiction of a gaseous fuel system.
• Embodiments of a gaseous or dual fuel electronic pressure regulation system (EPRS) for a multipoint fuel injection (MPFI) engine are described herein. Additionally, embodiments of a method for controlling the EPRS are provided.
• the EPRS employs an electronic pressure regulator (EPR) capable of accurately determining and controlling the mass flow of gaseous fuel into a fuel rail so as to avoid pressure droop and over- and under- pressurization of the gas admission valves (GAVs).
• EPR electronic pressure regulator
• GAVs gas admission valves
• using the disclosed EPRS provides another degree of freedom for controlling mass flow in a multipoint system.
• Conventional fuel control systems (such as those discussed above and shown in FIG. 8) have fixed supply pressures which can accentuate limitations of a MPFI system.
• mass flow is able to be controlled to the downstream manifold or engine cylinders very accurately, and the GAVs are able to be driven simultaneously in a pressure/pulse duration that is optimal for accurate and repeatable operation.
• Exemplary embodiments are provided by way of illustration and not by way of limitation. A person of ordinary skill in the art, upon consideration of the present disclosure, may recognize additional embodiments or modifications that fall within the spirit and scope of the present disclosure.
• FIG. 1 is a schematic representation of a gaseous EPRS 10 for an MPFI engine.
• gaseous fuel is supplied at a pressure Pi to the EPRS 10.
• an EPR 12 such as the TecJetTM series of fuel metering valves, available from Woodward, Inc., Fort Collins, Colorado determines and controls the flow of the gaseous fuel to provide a desired mass flow rate of the gaseous fuel into a fuel rail 14.
• to “determine” a parameter of the EPRS 10 may include directly measuring the parameter or estimating the parameter using mathematical models that consider, e.g., other directly measured parameters in the EPRS 10.
• the gaseous fuel is distributed from the fuel rail 14 through a plurality of GAVs 16 to the downstream manifold 18 or, in embodiments, directly to downstream engine cylinders (not shown).
• the GAVs 16 provide gaseous fuel to the manifold 18 via port injection, and in other embodiments, the GAVs 16 provide gaseous fuel to the cylinders via direct injection.
• a controller such as an engine control unit (ECU) 20, coordinates operation of the EPRS 10, including setting the mass flow rate of the EPR 12 and the duration of the GAVs 16.
• ECU engine control unit
• the ECU 20 provides the EPR 12 with a pressure demand and a GAV demand and supplies the EPR 12 with information regarding the gaseous fuel, such as the fuel specific gravity (SG) and the adiabatic index (g). Additionally, the ECU 20 receives various pressure readings from within the EPRS 10. In particular, the ECU 20 receives a GAV inlet pressure P 2 and a GAV outlet pressure, or a manifold absolute pressure (MAP), P 3 . While the system so described is a gaseous fuel system, the concepts discussed herein also apply to the gaseous component of a dual fuel system, such as a combination diesel and natural gas engine, in which the diesel fuel and the gaseous fuel are distributed on separate rails to an engine cylinder.
• a dual fuel system such as a combination diesel and natural gas engine
• FIG. 2 a simplified schematic representing the control method is provided in FIG. 2.
• the EPR 12, fuel rail 14, and a GAV 16 are provided along with variables associated with and/or sensed at each location.
• a temperature T and the pressure Pi are sensed at or near the EPR 12.
• the EPR 12 sets the mass flow rate (riiR) through the EPR 12 and into the fuel rail 14, which is determined, in part, by the effective area (AC C I) R for flow through the EPR 12.
• the fuel rail 14 has a known volume (V), and the pressure P 2 of the fuel rail 14 (which is also the GAV 16 inlet pressure) is sensed.
• the mass flow rate (rhv) through the GAV 16 and into the manifold 18 (as shown in FIG. 1), which is determined, in part, by the effective area (AC d )v for flow through the GAV 16.
• the EPR 12 is able to accurately control the mass flow of the gaseous fuel. Further, because of the ability of the EPR 12 to control mass flow, the ECU 20, as shown in FIG. 3, is able to simultaneously control mass flow (via the EPR 12) and pressure of the fuel rail 14 that supplies the GAVs 16 through the following embodiments of a control method.
• P2 f(Am r , rail geometry, gas properties) (3) wherein rim, (ACd)R, PI, P2, rhv, riiR, (ACd)v, and P3, are given above.
• Gas properties are the traditional macroscopic properties (pressure, volume (V), number of particles, temperature (T)) along with the thermodynamic properties of the gaseous fuel.
• Rail geometry is the physical dimensions of the fuel rail.
• P2 is the rate of change of pressure P2
• Am r is the mass flow rate imbalance in the fuel rail 14 that is a result of riiR being either greater or less than rhv.
• the mass flows riiR and rhv for the EPR 12 and the GAVs 16, respectively may be determined by several methods including the standard orifice flow equation, flow characterization of the valve, or using information stored in one of various databases (e.g., the NIST REFPROP database).
• the standard orifice flow equation for equations 1 and 2 above, an example of the standard orifice flow equation implementation of the /( ⁇ ) function given by:
• This function may be implemented directly, approximated, or accomplished via a lookup table.
• g is the adiabatic index.
• the ) function may be formulated in various ways. If ideal gas assumptions hold and the temperature and fuel composition is constant, P 2 may be expressed as a mass imbalance multiplied by a constant (e.g., Rs*T/V). However, this could also be modeled using thermodynamic properties and real gas properties. If rail dynamics are substantial, they could also be included in this model. If spatial dynamics are included, the modeled P 2 could be at any point in the rail.
• the control objective is to independently control both the mass flow through the GAVs 16 (through varying the pulse duration) and the pressure P 2 in the volume V of the fuel rail 14 independently.
• a general form of equations for AC d that accomplish this control objective are given by:
• FIG. 4 provides a schematic of a first order filter 30 for obtaining P 2 ref .
• the first order filter 30 has an input signal 32 corresponding to the commanded volume pressure P 2 set .
• the input signal 32 is summed with a feedback signal 34, which corresponds to P 2 ref , at summing point 36.
• the sum of the input signal 32 and the feedback signal 34 is provided to a buffer amplifier 38, and the output signal 40 of the buffer amplifier 38, which corresponds to P 2 ief , is one of the inputs for an integrator 42.
• the other integrator input 44 is the sensed pressure P 2 .
• P 2 ref and P 2 ref define the trajectory that volume pressure will actually follow.
• FIGS. 5-7 Exemplary embodiments of a hypothetical response of the EPRS 10 according to the first order filter 30 of FIG. 4 based on equations 4 and 5 are shown in FIGS. 5-7.
• the mass flow rhv through the throttle or GAVs 16 instantaneously changes from 35 kg/hr to 10 kg/hr.
• the filling volume of the EPR 12 adjusts P 2 without affecting mass flow rhv through the GAVs 16.
• the reference pressure P 2 ref is stepped down from 1.5 bar to 1.3 bar, and the actual pressure P 2 that is tracked by the system is seen dropping to the stepped down volume pressure of 1.3 bar.
• FIG. 5 Exemplary embodiments of a hypothetical response of the EPRS 10 according to the first order filter 30 of FIG. 4 based on equations 4 and 5 are shown in FIGS. 5-7.
• the mass flow rhv through the throttle or GAVs 16 instantaneously changes from 35 kg/hr to 10 kg/hr.
• the filling volume of the EPR 12 adjusts
• the concepts underlying the control scheme are extendable to actuators with finite bandwidth by ensuring that AC d values for the EPR 12 and the GAVs 16 are synchronized with the volume reference trajectory.
• Finite bandwidth limitations refer to two conditions.
• the EPR 12 and GAVs 16 take a non-zero amount of time to change effective areas.
• the actuator of the EPR 12 accelerates to move and decelerates to stop, i.e., the change in effective area (AC d ) R is not instantaneous.
• the GAVs 16 change effective area (AC d )v by changing pulse duration on a pulse-by -pulse basis.
• the change in pulse duration of the GAVs 16 is able to be coordinated with the change in effective area (AC d ) R of the EPR 12 over the timing of changing effective area (AC d ) R .
• the EPR 12 and GAVs 16 have absolute operational limits for effective area AC d .
• the EPR 12 is limited in movement between a fully open condition and a fully closed condition.
• the GAVs 16 have a maximum pulse duration and a minimum pulse duration needed to maintain delivery of fuel to the system.
• observing the finite bandwidth limitations is achieved by saturating the reference P 2 velocity, e.g., saturating P 2 ref (output signal 40) as shown in FIG. 4.
• the EPR 12 is configured to start changing the volume pressure P 2 before the GAVs 16 (or throttle) begin changing their effective area AC d .
• the EPR 12 leads the GAVs 16, which is something that conventional mechanical regulators, as described above, are unable to perform.
• the EPRS 10 as described herein provides for asynchronous control of the EPR 12 and the GAVs 16. That is, the effective areas (AC C I)R and (AC d )v are able to be changed independently at different times, or to put it differently, the effective areas (AC d )R and (AC d )v do not have to be changed at the same time.
• the aforementioned control method is implemented by adding an algorithm to the ECU 20.
• the algorithm computes in real time the state of the volume V of the fuel rail 14.
• the state parameter is defined by the pressure P 2 , and P 2 is determined based on the mass imbalance as defined in equation 3.
• State-based control in the EPRS 10 is able to be provided by combining the functionality of a mass control device with high accuracy mass flow monitoring and control. State-based control has the advantage of being user friendly in that such control allows for the user to input a simple demand, such as a desired mass flow, and the ECU 20 will configure the EPRS 10 in accordance with the demand.
• the ECU 20 receives a mass flow delivery command based upon engine requirements (e.g., speed, load, environment, etc.).
• the ECU 10 using the above-described algorithm, meets the exit mass flow command by changing the duration of the GAVs 16 utilizing the knowledge of the constant pressure P 2 of the fuel rail 14.
• the algorithm provides the ability to prescribe the pressure P 2 in the fuel rail 14 during the execution of a new mass flow set point by managing the pressure P 2 in the fuel rail 14 to a pressure set point that is used to accurately calculate the duration of the GAVs 16. Further, any mismatch in the actual mass flow to the target mass flow will manifest as a change in the pressure P 2 of the fuel rail 14.
• stabilization of the pressure P 2 serves as an indication that the mass flow rhv exiting the GAVs 16 matches the mass flow lii R entering the fuel rail 14 through the EPR 12.
• an EPR 12 is able to be used from a prognostics standpoint to determine when the GAVs 16 need to be serviced.
• the inlet mass flow controller in the EPR 12 is very accurate, the calibration constants of the GAVs 16 are able to be updated and saved at times of steady pressure (i.e., at times when the rate of pressure change is at or near zero) using the mass flow from the EPR 12, thereby enabling automatic recalibration during the life of the GAVs 16. Additionally, the present system and method help to prevent over-pressurization of the GAVs 16 during large transient events by using the EPR 12 to manage pressure. As an example of such a large transient event, during a full load rejection condition, the manifold absolute pressure could drop significantly, which would create a large differential pressure across the GAVs 16.
• a large pressure differential could be created during a shutdown event in which the shutoff valve is located well upstream of the fuel rail.
• the close coupling of the EPR 12 to the GAVs 16 allows for a faster reduction in the pressure P 2 of the fuel rail 14 during such events.
• Additional protection is provided to the GAVs 16 because the algorithm knows the upper and lower operability pressure limits (i.e., finite bandwidth limitations) of the GAVs 16 and is able to manage the pressure P 2 of the fuel rail 14 to stay within those operability limits by commanding temporary deviations in the inlet mass flow liiR. Similar protection is provided for the EPR 12 such that the EPR 12 operates within its finite bandwidth limitations to maintain accuracy of the EPR 12 and avoid damage. Thus, if the pressure P 2 is trending high, the inlet mass flow controller executes a temporary mass flow rate reduction/imbalance, such that the outflow exceeds the inflow and the pressure differential is negative.
• the inlet mass flow controller executes a temporary mass flow rate reduction/imbalance, such that the outflow exceeds the inflow and the pressure differential is negative.

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